The present invention relates to a single facer and a corrugating roll for a single facer.
An example of a conventional single facer (i.e., single faced corrugated board producing machine) is shown in FIG. 7. The single facer uses a pressure roll 3.
More specifically, a core paper 7 fed to the upper side of an upper corrugating roll 1 in a direction indicated by an arrow is delivered between a pair of an upper corrugating roll 1 and a lower corrugating roll 2. The upper corrugating roll 1 and the lower corrugating roll 2 have tooth forms in parallel with axes on circumferential portions thereof and are engaged with each other. The upper corrugating roll 1 and the lower corrugating roll 2 are rotated while the core paper 7 is fed in the engagement portion to thereby form the corrugation on the core paper 7.
The corrugated core paper 7 is transferred to a glue application roll 4 by the rotation of the lower corrugating roll 2. The glue application roll 4 performs the glue layer thickness control by a doctor roll 5, picks up glue contained within a glue container 6 and applies it to the top of the corrugation of the core paper 7.
The glue applied paper 7 is transferred to a pressure roll 3 by the rotation of the lower corrugating roll 2 and at the same time, a liner paper 8 is supplied to the pressure roll 3. The pressure roll 3 presses the liner paper 8 against the lower corrugating roll 2 and presses and adheres both papers to form a single-faced corrugated board 9.
Another example of the single facer is shown in FIG. 8. In this single facer, an endless pressure belt 10 is used instead of the pressure roll 3.
Since the pressure belt 10 simultaneously presses a plurality of teeth of the lower corrugating roll 2, it is possible to reduce a pressure between the core paper and the liner paper 8 in comparison with the pressure roll 3.
However, since the upper corrugating roll 1 and the lower corrugating roll 2 of the above-exemplified single facers have a tooth tip portion having a relatively small radius of curvature as shown in FIGS. 4 to 6, there have the following disadvantages.
More specifically, as shown in FIG. 4, the upper corrugating roll 1 and the lower corrugating roll 2 have the tooth portions in parallel to the roll axes on the roll outer circumferential portion of the radius R.sub.C of curvature. As shown in FIG. 5, their tooth profile of tooth portion is composed of three portions, i.e., a tooth tip portion, a tooth side portion and a tooth bottom portion.
The tooth tip portion includes a tooth apex portion S.sub.1 and is defined by an arc (S.sub.1 to S.sub.2) forming a part of a circle .epsilon. (indicated by a two-dotted and dash line in FIG. 5) having a relatively small radius of curvature.
The tooth side portion is defined by a straight line (S.sub.2 to S.sub.3) that is tangential with the circle .epsilon. at a terminal portion of the arc (S.sub.1 to S.sub.2) forming the tooth tip portion.
The tooth bottom portion is tangential at a terminal end portion S.sub.3 with the straight line (S.sub.2 to S.sub.3) forming the tooth side portion and is defined by a concave arc (S.sub.3 to S.sub.4) forming a part of a circle .zeta. (indicated by a two-dotted and dash line in FIG. 5) having a relatively small radius of curvature.
Thus, since the tooth tip portion of the lower corrugating roll 2 is defined by the arc (S.sub.1 to S.sub.2) having a relatively small radius of curvature, when the core paper 7 and the liner paper 8 are compressed between the lower corrugating roll 2 and the pressure roll 3 or the pressure belt 10, as shown in FIG. 6, a nip pressure W is applied between the tooth tip portion F of the lower corrugating roll 2 and the pressure roll 3 or the pressure belt 10, a pressure P having a sharp rise is applied to the paper E (i.e., the core paper 7 and the liner paper 8), and the maximum pressure is extremely increased.
If such a large local pressure is applied, not only a fracture of the paper is likely to be generated upon bonding but also a black pressure mark, called a press mark, is generated, to thereby permanent discoloring occurs even if the paper is not broken.
Accordingly, in the conventional corrugating roll, the paper fracture is very likely to occur upon bonding. Otherwise, the permanent discoloring, called a press mark, is generated to reduce a quality and a strength of the corrugated board. In addition, the conventional system has a disadvantage of generating a loss of paper to cause an economic problem. Also, a working efficiency is degraded.
Furthermore, in the above-described prior art, since the tooth tip portion has a relative small radius of curvature for the upper and lower corrugating rolls 1 and 2, it also has a disadvantage that the machining work is troublesome.
For example, upon machining the upper corrugating roll 1 and the lower corrugating roll 2, if, first of all, the roll form having a radius R.sub.C is machined and the tooth portion composed of the tooth tip portion, the tooth side portion and the tooth bottom portion in parallel to the roll axis on the roll outer circumferential portion, since the arc having the relatively small radius of curvature has to be formed as the tooth tip portion, the number of the machining steps is increased, as a result of which the manufacturing cost is increased.